Sulfur dioxide-releasing device

ABSTRACT

A device for preserving fresh fruit by releasing sulfur dioxide into a sealed container of the fruit. The device comprises a layer of solid coating material and a particulate compound forming a substantially uniform dispersion throughout the layer. The compound is characterized by the release of sulfur dioxide on contact with water vapor. One device is formed of a dispersion of sodium bisulfite in a layer of white scale paraffin wax containing a viscosity-increasing agent.

United States Patent 1 1 3,559,562

[72] Inventors Herbert E. Carlson [56] References Cited Fort tar-age,N.C-: UNITED STATES PATENTS 3,409,444 ll/l968 Gentry .1 99 171 [21] AppLNo. 831,181

[22] Filed June 6,1969

[45] Patented Feb. 2, 1971 [7 3 Assignec Boise Cascade CorporationBoise, Idaho a corporation of Delaware [54] SULFUR DIOXIDE-RELEASINGDEVICE 15 Claims, 4 Drawing Figs.

[52] U.S.Cl 9 9/239,

99/154 [51] ,-lnt.Cl A23b 7/00 {50] Field of Search 99/154,

. 1 1 nAnn u nn unn 1,575,148 3/1926 Carbone... 99/269 2,929,761 3/1960Stevens 99/ l 54 3,346,398 10/ l 967 Tundermann 99/ l 54 3,450,5426/1969 Badran 99/154 Primary Examiner-Robert W. Jenkins Attorney-Flehr,Hohbach, Test, Albn'tton & Herbert ABSTRACT: A device for preservingfresh fruit by releasing sulfur dioxide into a sealed container of thefruit. The device comprises a layer of solid coating material and aparticulate compound forming a substantially uniform dispersionthroughout the layer. The compound is characterized by the release ofsulfur dioxide on contact with water vapor. One device is formed of adispersion of sodium bisulfite in a layer of white scale paraffin waxcontaining a viscosity-increasing agent.

PATENTEUFEB2 lsn IN VENTOR.

' Herbert E. Carlson By Rodrick E. Black zforneys SULFURDIOXIDE-RELEASING DEVICE BACKGROUND OF THE INVENTION In one techniquefor storing fresh fruit. such as picked grapes, the fruit is packed inopen wooden lugs or corrugated cases with vent holes and placed in acold storage room. Sulfur dioxide gas is introduced into the room andpermeates through the containers to the grapes in an attempt to preventthe growth of microorganisms, such as mold. The gas concentration mustbe closely regulated throughout the storage period. An excess of gastends to injure the fruit, while an insufficient quantity permits moldto grow on the fruit. Moisture in the fruit vaporizes during storagesince the containers are open. This dehydration leads to a loss ofquality and appearance of the fruit. Another problem is that highconcentration of the corrosive sulfur dioxide gas deteriorates equipmentin the cold storage rooms.

In another storage technique, the fresh fruit at ambient temperatures isplaced in moisture-tight boxes having a self-contained source of sulfurdioxide gas and the boxes are deposited in a cooling room. The moisturecontent of the fruit is retained in the container, tending to minimizedehydration deterioration of the fruit. To prevent the rapid growth ofmold before the fruit has cooled completely. a relatively highconcentration of sulfur dioxide gas must be emitted. The highconcentration is necessary to prevent the fast growth of mold on thefruit which occurs at the warm, high humidity conditions prevalent inthe essentially-sealed containers. When the fruit has reached the coldstorage temperature, the quality of sulfur dioxide should be decreasedto a steady, lower level for the duration of storage for two reasons:firstly, mold grows more slowly at this temperature, and, hence, lesssulfur dioxide is necessary; secondly a high level of sulfur dioxide forprolonged periods of time will result in a deterioration of the fruit.

The technique of the preceding paragraph has been carried out by amethod employing two different types of envelopes enclosing an agent,such as sodium bisulfite, that releases sulfur dioxide on contact withwater vapor. The sodium bisulfite is in loose form. These envelopes areplaced within the sealed containers. One type of envelope is readilypermeable by moisture and, hence, rapidly releases sulfur dioxide. Thesecond envelope, being less permeable by moisture, releases the sulfurdioxide more slowly than the first envelope. Since these two types ofenvelopes are required in each container, instructions must be given tothe fruit packers and there is the possibility of the human error ofomission of one or the other of the envelopes. In addition, the twodifferent envelopes are costly to produce and the manufacture must beunder close tolerances to emit predetermined amounts of sulfur dioxide.Furthermore, these envelopes release sulfur dioxide in a concentratedarea of fruit adjacent to the envelopes. Hence, these fruits are subjectto deterioration caused by exposure to an excessive concentration ofsulfur dioxide gas.

SUMMARY OF THE INVENTION AND OBJECTS This invention relates to a devicefor releasing sulfur dioxide under controlled conditions into asubstantially sealed container of fresh fruit, such as grapes, tomaintain the fruit in its freshly-picked condition over extended periodsof time. The

, device comprises a coating of material on a sheet, such as In oneembodiment of the invention. the device is coated on a paper sheet andinserted inside a fruit cushioning pad which. in turn. is positioned ina sealed fruit container. Alternatively, the coating may be formed onthe internal surface of the cushioning pad. In a further alternative.with a corrugated case as the container, the device may form part of thecontainer water vapor barrier. With wooden lugs as the containers, thedevice may be placed on a liner which may be used therein as a containerseal.

Accordingly it is an object of the invention to provide an improveddevice for treating fresh fruit to preserve the fruit over extendedperiods of time, which device eliminates the deficiencies of theaforementioned fruit-treating methods.

It is another object of the invention to provide an improved device forreleasing sulfur dioxide under controlled conditions into asubstantially sealed container.

It is a further object of the invention to provide a single source ofsulfur dioxide to be released under controlled conditions into asubstantially sealed container of fresh fruit to thereby preserve thefruit over extended periods of time.

It is a further object of the invention to provide an economical.readily produced device that releases sulfur dioxide under controlledconditions without the requirement of close regulation in manufacture.

It is a further object of the invention to provide a device forreleasing sulfur dioxide uniformly along the entire internal surface orsurfaces of a sealed container rather than releasing in concentratedpockets thereof.

Other and further objects of the invention will be more apparent fromthe following description taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view acrossa vertical plane through a fresh grape container according to thisinvention;

FIGS. 2 and 3 are enlarged cross-sectional views of cushioning padsaccording to this invention;

FIG. 4 is a wooden lug lined with a paper barrier incorporating thisinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1,the device of the invention may be placed within a container 1 1 havinga lower portion 12 with a bottom 13 and an upper portion 14 with a top16. The container is suitably of rectangular shape and fabricated ofsuch material as fiberboard or a corrugated sheet and coated with amoisture vapor barrier. Portions l2 and 14 form a snug fit so that whenthe container is assembled, there is little leakage of air into, ormoisture out of, the container.

According to the invention, grapes 17, or other fresh fruit, are storedwithin the sealed container 11. The container is provided with top andbottom cushioning pads 18 and 19, respectively. In one embodiment, thecushion has a liner 20, suitably formed on treated paper, folded over atthe ends 21 and 22 to provide a cavity. A filling 23, suitably of amaterial such as redwood bark, excelsior, or shredded paper, is placedin the cavity. The filled pad provides resilience to afford shockresistance and to accommodate irregularities.

A particular embodiment of a cushioning pad is shown in FIG. 2. Placedwithin the pad is a sheet 24, of a material such as paper, coated with asolid layer 25 having an exposed surface 26. A substantially uniformdispersion of particles 27, which serve to release sulfur dioxide oncontact thereof with moisture, is formed within the layer. Layer 25dispersed with particles 27 and coated on a surface will be designateddevice 28 hereinafter. Layer 25 must be capable of coating sheet 24 in aviscous fluid state while retaining particles 27 uniformly dispersedtherein. Furthermore, the coating must have the ability to hardenwithout displacement of the uniform particu' late dispersion.

In one device 28. a dispersion of a binder and solvent is mixed withparticles 27 and coated upon the sheet 24. When the solvent evaporates.the particles remain in a uniform dispersion in the binder. Suitablebinders are lacquers or resins such as: ethyl cellulose, celluloseacetate, cellulose acetate butyrate, and polyvinylidene halides.

In another device 18. layer 25 is suitably formed from a major portionof a wax and a minor portion of an agent to increase the wax viscosity.Suitable waxes are parafi'm wax, such as scale wax, microcrystallinewax, and various synthetic and naturally occurring waxes. The agent isfirst dissolved in molten wax and the particles uniformly dispersed intothe solution. The molten mixture is then coated on a sheet by suitablemeans such as spreading with a wire-wound rod to a weight sufficient tocoat the desired amount of particles. Another suitable coating methodwould be performed in a standard curtain coater.

Suitable viscosity-increasing agents for the wax must be compatible withthe wax in the concentrations used. For ex ample, polymers such aspolymono-olefins. ethylene vinyl acetate copolymers, butyl rubber,butadiene-styrene rubber. and ethylene vinyl acrylate copolymers andterpolymers may be used. A suitable ratio of wax to viscosity-increasingagent is from about 2 to l parts by weight to about 8 to l by weight.

Particles 27 may be formed of any compound which releases sulfur dioxideupon contact with water vapor. The compounds are suitably chosen fromthe group: sodium bisulfite, sodium sulfite-fumaric acid mixture, sodiumsulfitepotassium bitartrate mixture, and combinations thereof. Otherheat-stable acids and acid salts may also be used.

The size of the particles 27 has an important effect on the release rateof the sulfur dioxide in the layer 25. The release rate is proportionalto the size of the particles. This is apparent since grinding theparticles to a smaller size permits a greater amount of coating materialto surround the particles which inhibits the release of sulfur dioxide.It has been found that a uniform release is obtained from particles of asize distribution as follows: about 25 to 40 percent of the particlespassing through a 100 mesh screen, but not through a 200 screen; aboutto 25 percent of the particles passing through a 200 mesh screen but notthrough a 325 mesh screen; and the remainder of the particles passingthrough a 325 mesh screen.

Another factor in the release rate of sulfur dioxide is theconcentration of particles in the coating. Increasing the amount ofparticles in the coating leads to a correspondingly increased releaserate since there is less coating material to inhibit the contact of theparticles with moisture. For normal grape storage, a suitable ratio ofparticulate compound to coating material is from about 5 to l to about 1to 5.

A further factor influencing the sulfur dioxide release rate and thelength of time for release is the thickness of the coating. A thickercoating yields a slower and more prolonged release since the moisturetakes a longer time to reach particles as they are further removed fromthe exposed surface. A suitable coating thickness has been found to beabout 7 to l2 mils for release on the order of several weeks to severalmonths.

Another factor in the rate of sulfur dioxide release is thepermeability, of the material used as the particle coating, to watervapor. The more permeable the material, the faster is the sulfur dioxiderelease rate.

During storage, grapes at ambient temperatures are placed in a number ofcontainers 11 and deposited in a cold storage room. When the water vaporpermeates the cushion pad and deeply into the coating. Consequently.sulfur dioxide gas is slowly released over a long period of time. suchas over three months. in sufficient quantities to inhibit the growth ofmold while maintaining a level of sulfur dioxide sufficiently low to notinjure the grapes.

Although there is no intention to be limited by any particulartheoretical explanation for the prolonged, substantially steady releaseof sulfur dioxide, one possible explanation for this phenomenon could bea channelling" effect. It is possible that various particles touch orcome quite close to touching various other particles in layer 25 to forman almost continuous bridge of particles. As the particles are consumedby reaction with water vapor, a three-dimensional channelling. 0rhoneycomb. effect is produced whereby particles positioned more deeplyin the coating become successively available for reaction with the watervapor. Thus, at any time after the initial reaction of particles at thesurface of the layer an approximately equal number of particles areexposed for reaction with the water vapor.

It is noted that sulfur dioxide is released along the entire surface ofthe device and. therefore, the cushioning pads. This results in asubstantially uniform concentration of sulfur dioxide in any area of thegrapes, thus avoiding the risk of deterioration of grapes caused byexcessive sulfur dioxide exposure.

Referring to FIG. 3, in another cushioning pad. device 28 is coateddirectly on the internal surface of liner 20. This eliminates thenecessity for the insertion of a secondary coated sheet into the cushionpad as in the embodiment of FIG. 2.

Referring to FIG. 4. wooden lug boxes 29 may be used instead ofcontainer 11 to store the fruit. These lug boxes normally containperforations 30 for ventilation. Therefore, in order to form a moistureseal for the box, a liner 31 is placed on all internal surfaces of thebox. According to the invention device 28 may be coated on liner 3] in asuitable manner as above described. Using the coated liner on allinternal surfaces of the box, sulfur dioxide is released uniformly forfrom all directions to the grapes. This type of release is even afurther safeguard than the cushions against a high concentration ofsulfur dioxide to damage exposed grapes.

In another embodiment of the invention (not shown), cushioning pads'l8and 19 contain no sulfur dioxide releasing device. Device 28 is directlycoated on the internal surfaces container 11 immediately adjacent to thegrapes 17. The sulfur dioxide is released from all directions as in thepreceeding paragraph.

The following examples serve to describe several specific embodiments ofthe invention.

EXAMPLE 1 A sulfur dioxide-releasing coating was prepared according tothe invention. Elvax 260 a duPont trademark for an ethylene vinylacetate copolymer (25.5 grams), was dissolved in 124.5 grams of moltenscale wax (melting point of 128- 1 30 F.) at a temperature of 300 F.After cooling the solution to 200 F ground sodium bisulfite was stirredinto the solution to form a uniform particulate mixture. The mixture,maintained at 200 F., was coated on paper by means of a wire-wound roduntil about 7 grams of sodium bisulfite was coated on an area equal to acushioning pad main surface. This is a concentration of approximately 12pounds of sodium bisulfite per l,000 square feet of paper. After thecoating was cooled to room temperature and solidified, it was placed asan insert into the cushioning pad.

Two of these cushioning pads containing 7 grams of sodium bisulfiteeach, were placed in a standard sealed corrugated box containing 26pounds of fresh grapes at ambient temperatures. The boxes were placed incold storage (at about 32 F.) for a period of about three months. Whenthe boxes were opened, no substantial deterioration had occurred.

EXAMPLE 2 The same coating procedure and ingredients in the coating wereused as in Example I. The only change was the ratio of components.Sodium bisulfite (100 grams) was dispersed in a solution of 17 grams ofElvax 260 in 83 grams of scale wax (melting point l28l30 F.). Althoughthe same concentration of 14 grams sodium bisulfite to 28 pounds ofgrapes was used, there was less wax coating on the sodium bisulfiteparticles resulting in a faster release of sulfur dioxide. After aboutfour weeks of grape storage as in Example 1, the grapes would be in thesame condition as when freshly picked.

EXAMPLE 3 The same procedure as in Example 1 was used with the followingformula for the device: 68 grams of scale wax (128- l30 F. meltingpoint), 14 grams of Elvax 260, 62 grams of sodium sulfite, 56 gramsfumaric acid. The fumaric acid and sodium sulfite react on contact withmoisture to produce sulfur dioxide.

Grapes stored with the above coating in the concentration of 14 grams ofsulfur dioxide-releasing agent per 28 pounds of grapes maintained thegrapes in a fresh condition for over I month.

EXAMPLE 4 Following the procedure of Example 1, an equal weight ofsodium bisulfite may be dispersed in a commercial cellulose acetatebutyrate lacquer and coated on paper with the solvent being driven offby a low heat. This coated paper would be inserted into a cushioning padas in Example l and should yield sufficient quantities of sulfur dioxidefor at least 3 weeks.

It is apparent from the foregoing description that the amount of activesulfur dioxide-releasing agent used per pound of grapes to be stored maybe suitably varied to accommodate changes in the amounts of storage timerequired. Also, the concentration of release agent in the coating can bemodified to control the rate of sulfur dioxide gas released from thecoating.

We claim:

1. A device for preserving fresh fruit by releasing sulfur dioxide undercontrolled conditions into a substantially sealed container of thefruit, said device comprising a layer of solid coating material and aparticulate compound characterized by the release of sulfur dioxide uponcontact with water vapor, said compound forming a substantially uniformdispersion throughout said layer, said device serving to quickly releasesulfur dioxide on initial contact with water vapor and more slowly andsteadily release sulfur dioxide thereafter for extended periods of time.

2. A device as in claim I wherein a mixture of said coating materialincludes a major portion of scale wax and a minor portion of aviscosity-increasing agent.

3. A device as in claim 2 wherein the binder is selected from the groupconsisting of polymono-olefins, ethylene vinyl acetate copolymers, butylrubber, butadiene-styrene rubber,

and ethylene acrylate copolymers and terpolymers.

4. A device as in claim 2 wherein the ratio of scale wax to agent isfrom about 2 to l to about eight to one parts by weight.

5. A device as in claim 1 wherein said coating material is a lacquer.

6. A device as in claim 5 wherein said lacquer is selected from thegroup consisting of ethyl cellulose, cellulose acetate, and celluloseacetate butyrate, and polyvinylidene halides.

7. A device as in claim 1 wherein said compound is selected from thegroup consisting of sodium bisulfite, sodium sulfitefumaric acidmixture, sodium sulfite-potassium bitartrate mixture and combinationsthereof.

8. A device as in claim 1 wherein the ratio of particulate compound tocoating material is from about 5 to l to about l to 5 [R weight.

9. device as in claim 1 wherem the fruit 18 grapes and the extended timeperiod is over 3 months.

10. A device as in claim 1 coated on a pliable base sheet which isinserted into a fruit cushioning pad.

11. A device as in claim 1 coated on the inside of a fruit cushioningpad.

12. A device as in claim 1 coated on the inside of the sealed containerand forming at least a portion of the seal therefor.

13. A device as in claim I coated on a box liner used as a barrier toseal the container.

14. A device as in claim I wherein at least 30 percent of theparticulate compound passes through a 325 mesh screen.

15. A device for releasing sulfur dioxide under controlled conditionsinto a substantially sealed container of fresh grapes, said devicecomprising a layer of solid coating material of about 7-l2 milthickness, formed of a mixture of a major portion of scale wax and aminor portion of a binder to increase the wax viscosity, finely groundsodium sulfite particles fon'ning a substantially uniform dispersionthroughout said layer, said device serving to quickly release sulfurdioxide on initial contact with water vapor and more slowly and steadilyrelease sulfur dioxide for at least 2 months.

2. A device as in claim 1 wherein a mixture of said coating materialincludes a major portion of scale wax and a minor portion of aviscosity-increasing agent.
 3. A device as in claim 2 wherein the binderis selected from the group consisting of polymono-olefins, ethylenevinyl acetate copolymers, butyl rubber, butadiene-styrene rubber, andethylene acrylate copolymers and terpolymers.
 4. A device as in claim 2wherein the ratio of scale wax to agent is from about 2 to 1 to abouteight to one parts by weight.
 5. A device as in claim 1 wherein saidcoating material is a lacquer.
 6. A device as in claim 5 wherein saidlacquer is selected from the group consisting of ethyl cellulose,cellulose acetate, and cellulose acetate butyrate, and polyvinylidenehalides.
 7. A device as in claim 1 wherein said compound is selectedfrom the group consisting of sodium bisulfite, sodium sulfite-fumaricacid mixture, sodium sulfite-potassium bitartrate mixture andcombinations thereof.
 8. A device as in claim 1 wherein the ratio ofparticulate compound to coating material is from about 5 to 1 to about 1to 5 by weight.
 9. A device as in claim 1 wherein the fruit is grapesand the extended time period is over 3 months.
 10. A device as in claim1 coated on a pliable base sheet which is inserted into a fruitcushioning pad.
 11. A device as in claim 1 coated on the inside of afruit cushioning pad.
 12. A device as in claim 1 coated on the inside ofthe sealed container and forming at least a portion of the sealtherefor.
 13. A device as in claim 1 coated on a box liner used as abarrier to seal the container.
 14. A device as in claim 1 wherein atleast 30 percent of the particulate compound passes through a 325 meshscreen.
 15. A device for releasing sulfur dioxide under controlledconditions into a substantially sealed container of fresh grapes, saiddevice comprising a layer of solid coating material of about 7-12 milthickness, formed of a mixture of a major portion of scale wax and aminor portion of a binder to increase the wax viscosity, finely groundsodium sulfite particles forming a substantially uniform dispersionthroughout said layer, said device serving to quickly release sulfurdioxide on initial contact with water vapor and more slowly and steadilyrelease sulfur dioxide for at least 2 months.